As this applies to Business Aircraft: When is “Old”, Too “Old?”

The oldest pyramid at 4,639 years is the Step Pyramid of Djoser built in the desert twelve miles south of Cairo near Saqqara, Egypt. The oldest standing structure, a temple in Malta is 6,000 years old. The oldest archaeological remains of a structure found in Japan, dates back to 500,000 years ago. The Grand Canyon is somewhere around 2,000,000,000,000 years old.

The oldest machine that is still functioning is reputed to be either a waterwheel in Spain, at about 1,300 years, or a clock in England that is 620 years old, or so. The oldest aircraft that is still flown today is a 1909 Bleriot (The Shuttleworth Collection in England, and Old Reinbeck Aerodrome here in the USA.) The oldest turbo-propeller aircraft still in operation are a handful of early 1950’s Vickers Viscount aircraft. The oldest business jet aircraft that are still in operation includes: several 1964 Rockwell Sabreliner 40 aircraft (including serial number 001), two 1965 Learjet 23 aircraft, a handful of 1965 and 1966 Hawker 1A aircraft, a slew of 1965 and up Dassault Falcon 20 aircraft, a 1967 Lockheed Jetstar TFE731 converted aircraft, and several 1968 ‘dash-eight’s’ Jetstar aircraft.

The 1977 crash of the Zambia Airways leased B707 was the first major commercial aircraft accident that was caused by age and metal fatigue. The horizontal stabilizer spars were fatigue cracked, and after inspection, more than fifteen percent of the ‘then’ in-service fleet were found to have the same problems that brought down the Zambia aircraft. Eleven years later when the Aloha airlines accident took place in 1988, where unnoticed corrosion caused an explosive decompression of a Boeing 737 while in-flight, immediately converting the subject aircraft into an ‘open-top’ vehicle, had rocked the aviation industry. Mainly thanks to the over-built strength that was inherent in the design of the B737 which allowed the damaged aircraft to make a safe landing, the Federal Aviation Administration (FAA) immediately leapt into action and created an ‘Ageing Aircraft’ Task Force to review the technical issues that were the result of aircraft ageing in service.

Apart from issues with the embrittlement of conductors and the breakdown of insulation in electrical wiring; crack formation and growth within some metal structures caused by stress and/or corrosion, the FAA found that the majority of ageing issues found in older aircraft were more likely to be serious in areas that had been structurally modified or repaired. Technically speaking, there is still no physical ‘across the board’, industry-wide hourly or calendar limit that is either required or implemented. In simple terms, there is little to no “too old” in aircraft design. Obviously then this becomes an issue of economics only, whereby the useful age of an aircraft is reached, when economic gain is either lost or significantly reduced.

The airlines target at least 3,000 hours per annum for their business model, hence that the target retirement/scrap age of most commercial passenger airliners starts around 60,000 hours and pushes as high as 90,000 hours. The business jet fleet truly falls under the ‘boutique’ category of aviation because it is rare for any business jet to fly more than 400 hours per annum. 30,000 hour business jet aircraft are highly unusual, especially in a field where 14,000 hours is considered ‘high-time’, and a fleet snapshot returns an average of 4,115 hours total-time-in-service for the majority of the active fleet. “So when is a Business Jet too old?” Is it now time for us to accelerate the natural attrition of “old” business jets as the older members of the ageing fleet are laid to rest

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